A popular and controversial sports supplement widely sold in the USA and other countries is secretly spiked with a chemical similar to methamphetamine that appears to have its origins as an illicit designer recreational drug, according to new tests by scientists in the USA and South Korea.

The test results on samples of Craze, a pre-workout powder made by New York-based Driven Sports and marketed as containing only natural ingredients, raise significant health and regulatory concerns, the researchers said.

The U.S. researchers also said they found the same methamphetamine-like chemical in another supplement, Detonate, which is sold as an all-natural weight loss pill by another company: Gaspari Nutrition.

"These are basically brand-new drugs that are being designed in clandestine laboratories where there's absolutely no guarantee of quality control," said Pieter Cohen, an assistant professor at Harvard Medical School and a co-author of the analysis of Craze samples being published today in the peer-reviewed scientific journal Drug Testing and Analysis.

"It has never been studied in the human body," Cohen warned. "Yes, it might make you feel better or have you more pumped up in your workout, but the risks you might be putting your body under of heart attack and stroke are completely unknown."

Craze, which is marketed as giving "unrelenting energy and focus" in workouts, was named 2012's "New Supplement of the Year" by Bodybuilding.com. A USA TODAY investigation published in July reported on other tests detecting amphetamine-like compounds in Craze.

While Walmart.com and several online retailers have stopped selling Craze in the wake of USA TODAY's investigation, the product has continued to be sold elsewhere online and in GNC stores. In recent weeks, Driven Sports' website, which offers Craze for sale, has said the product is out of stock. Detonate is sold by a variety of online retailers.

An attorney for Driven Sports, Marc Ullman, said the company had no comment on the latest findings that the compounds are actually more closely related to methamphetamine.

"We have previously provided USA Today with a plethora of data from a DEA Certified Lab indicating the absence of any amphetamine-like compound in Craze," Ullman said in an e-mail. "In light of USA Today's decision to ignore the data we have provided, we respectfully decline to comment for your story."

Officials at Gaspari Nutrition in Lakewood, N.J., did not respond to interview requests.

Because of the government shutdown, officials with the U.S. Food and Drug Administration, which oversees dietary supplements, could not be reached for comment. Calls to the Drug Enforcement Administration also weren't returned.

Cohen said researchers informed the FDA in May about finding the new chemical compound in Craze. The team found the compound - N,alpha-diethylphenylethylamine - has a structure similar to methamphetamine, a powerful, highly addictive, illegal stimulant drug. They believe the new compound is likely less potent than methamphetamine but greater than ephedrine.

"There are suggestions about how it's tweaked that it should not be as addictive as meth," Cohen said. But because it hasn't been studied, he said, its dangers aren't known. The team said it began testing Craze in response to several failed urine drug tests by athletes who said they had taken Craze.

Driven Sports has issued repeated statements in recent months that Craze does not contain any amphetamine-like compounds, including posting test results on its website that it says prove the product is clean. In July, a USA TODAY investigation revealed that a top Driven Sports official - Matt Cahill - is a convicted felon who has a history of selling risky dietary supplements, including products with ingredients linked to severe liver injury and at least one death. Cahill is currently facing federal charges in California involving his introduction of another supplement, Rebound XT, to the market in 2008 that contained an estrogen-reducing drug, and this spring a grand jury was also investigating, USA TODAY has reported.

The newspaper's investigation, which focused on several products sold over the years by Cahill's changing series of companies, reported that tests by the U.S. Anti-Doping Agency in June 2012 and a government-affiliated forensic lab in Sweden in April 2013 had detected undisclosed amphetamine-like compounds in samples of Craze.

A month after USA TODAY published its report about Cahill and Craze, a team of South Korean scientists published an article in a journal of the Japanese Association of Forensic Toxicology saying they had found a methamphetamine-like compound in samples of Candy Grape flavor and Berry Lemonade flavor Craze.

The researchers, from the National Forensic Service in South Korea and the National Institute for Public Health and the Environment in the Netherlands, noted that the compound found in Craze was the same as that found in a crystalline powder seized by narcotics agents in December 2011 as a suspected illicit designer drug. In that case the powder was found in an unclaimed lost package shipped from Vietnam to South Korea, according to an earlier journal article published by the team in late 2012. "It appeared that the recipient of this article sought to abuse this chemical in the same way as amphetamines. There is a possibility that this chemical will be widely abused for recreational use in the near future," they wrote at the time.

Instead, the same team soon found the compound in Craze.

The researchers noted that the compound had been patented in 1988 by Knoll Pharmaceuticals with claims of psychoactive effects, such as enhancing mental activities and pain tolerance. While it was never developed into a medicine, the patent described tests on animals and suggested an intended oral dose of 10 mg to 150 mg, with a target of 30 mg.

A suggested serving size of Craze yielded a dose of the compound of about 23 mg, the Japanese journal article said, and "it could be assumed that NADEP was added to the supplements intentionally for its pharmacological effects without adequate labeling."

The U.S. research team also found the meth-like substance at levels of 21 mg to 35 mg per serving in each of the samples tested from three separate lots of Craze.

Craze's label does not disclose the compound found by the researchers. Instead it says the product contains dendrobium orchid extract that was concentrated for different phenylethylamine compounds. Phenylethylamines include a variety of chemicals "that range from benign compounds found in chocolate to synthetically produced illicit drugs," according to the U.S. researchers.

The U.S. researchers noted that an "extensive" search of scientific literature does not find any evidence that the compound listed on Craze's label has ever been documented as a component of dendrobium orchid extract. The U.S. research team included Cohen; John Travis, a scientist at NSF International, a Michigan-based testing and standards organization that has a dietary supplement certification program; and Bastiaan Venhuis of the National Institute for Public Health and the Environment in the Netherlands.

Although not part of the journal article being published today, NSF International announced that in separate testing they also have detected the same methamphetamine-like compound in the weight-loss supplement Detonate sold by Gaspari Nutrition. "Regulators may want to consider taking action to warn consumers," NSF International said in a statement. Gaspari markets Detonate as containing "dendrobium extract."

Last year Driven Sports posted a series of blog items on its website alerting customers that counterfeit versions of Craze were being sold. "Could there be counterfeit products, of course," Cohen said. "Chances are this is more likely an effort by the manufacturer to distract regulators and consumers from what's really going on here."